1. Field of the Invention
This invention relates generally to a muffler for quieting the exhaust from an internal combustion marine engine, and, more particularly, to an improved lift muffler which permits the exhaust outlet therefrom to be placed in line with, or at a lower level relative to, the exhaust inlet to widen the range of positions and applications in which a lift muffler may be used, and to provide a lift muffler having a reverse flow water surge protector.
2. Description of the Prior Art
The exhaust of the typical marine vessel is directed through either the drive system in an inboard/outboard unit or simply through the transom in a inboard drive setup. Both applications place the exhaust outlet near or below the water line leading to possible back flow situations when the exhaust gas does not present enough force to overcome a water surge, or where water enters the exhaust pipe while the engine is off. To prevent this back flow of water into the muffler or engine, a check valve or flapper valve is visually employed. However, flapper valves, having moving parts, quickly corrode and fail, leading to a potentially dangerous blockage of exhaust flow.
There are a variety of marine mufflers presently known in the art which are of the "axial flow" type such as the muffler disclosed in U.S. Pat. No. 4,167,987, issued to Turner. The Turner patent describes a multiple flow marine muffler wherein exhaust noise is attenuated by passing the exhaust gas through a series of longitudinally spaced opposing baffles. Although the device allows an in-line connection, such a configuration requires an elongated cylindrical shell to provide the required baffling effect, thus precluding application in tight-fit areas such as smaller boats or other situations where space is at a premium. The use of an axial flow muffler does not address the need to counter water surges. Also, axial flow mufflers cannot be placed below the water line without some form of surge suppression.
Another marine muffler, known as a "lift muffler," is disclosed in U.S. Pat. No. 3,296,997, issued to Hoiby, et al. The Hoiby muffler is essentially an up-right drum-shaped housing having an exhaust inlet near the top and a stand pipe exhaust outlet centrally located with its opening spaced above the drum bottom. The stand pipe directs the muffled exhaust gas and collected cooling water upwardly and outwardly to a location where it can be discharged from the boat without further back pressure. Such a device precludes application in tight-fit areas as the centrally located stand pipe requires exhaust conduit modifications to accommodate the pipe. Further, Hoiby does not present a means to prevent a reverse flow of water when the exhaust outlet is submerged.
Another type of marine muffler is disclosed in U.S. Pat. No. 4,917,640, issued to Miles. Miles teaches the use of a marine muffler wherein the engine exhaust is displaced between chambers through a series of parallel conduits transverse to the muffler body length. Cooling water from the exhaust manifold is entrapped at the bottom of the main chamber, a portion thereof remaining in the chamber, the remainder of which accompanies exhaust gas out of the muffler body. The exhaust noise is attenuated by baffling the exhaust gas through multiple chambers and in contacting the entrapped water. However, this type of muffler is not amenable to mounting within the boat hull without elaborate piping geometry so that the muffler can be fed at the top and evacuated at the bottom.
Muffler outlet placement close to, or beneath, the water line requires a means for preventing the back flow of water caused by water surges occasioned by water currents striking the transom. Conventional lift mufflers employ only a horizontal baffle which cannot counter cause the drain-off of surge water.
Therefore, there exists a need for a muffler capable of installation within a boat hull wherein the exhaust inlet and outlet may be situated at the same level to permit in-line placement thus providing the benefits of a lift muffler having an in-line hookup. Further, there exists a need to prevent back flow of water into a lift-type muffler without the addition of a check or flapper valve